1. Field of the Invention
The present invention relates in general to a feeding device to be incorporated in an image reading apparatus equipped with an image reader which is operable to read an image on an original in a predetermined reading position while the original is being fed by the feeding device. More particularly, the invention is concerned with a feeding device defining a feed path by which the original takes, after having passed the reading position, a posture inclined with respect to an original supporting surface of the image reading apparatus.
2. Discussion of Related Art
In general, in an image reading apparatus capable of reading an image carried by an original which is being currently moved or fed as well as an image on an original which is held stationary there are provided two different transparent plates, one of which serves or taking the image on the currently fed original, and the other of which serves for taking the image on the stationary original. It is common that the two transparent plates are provided on an upper surface of a main body of the image reading apparatus (which surface is exposed when a cover body disposed on the upper surface is open) such that the two transparent plates are arranged in a longitudinal direction of the main body of the image reading apparatus. The transparent plate for the image on the stationary original has a size (as measured in the longitudinal direction of the main body of the image reading apparatus) which is as large as a length of an original having a maximum size acceptable by the image reading apparatus. The original is disposed on an upper surface of the transparent plate, so that the image on the stationary original is taken or read by an image reader which is moved along a lower surface of the transparent plate. On the other hand, the transparent plate for the image carried by the fed original has a size (as measured as in the longitudinal direction of the main body of the image reading apparatus) smaller than the above-described size of the transparent plate for the stationary original. The image of the fed original is read, when the original passes over an upper surface of the transparent plate, by the image reader which is held stationary below a lower surface of the transparent plate.
For improving an accuracy in reading the image on the original the stationary original can be pressed onto the upper surface of the transparent plate, by closing the above-described cover body. For the same purpose, the fed original is brought into contact or proximity with the upper surface of the transparent plate, when the original passes over the upper surface of the transparent plate. As a mechanism for bringing the fed original into contact or proximity with the upper surface of the transparent plate, JP-U-H01-100140 (publication of unexamined Japanese Utility Model laid open in 1989) discloses a holder plate which is disposed above the transparent plate and which is biased downwardly toward the transparent plate. The holder plate has spacers provided on its lower surface such that the spacers are positioned in such positions that do not interfere feed movement of the original. Owing to the provision of the spacers, the holder plate can be positioned above the transparent plate, with a constant spacing gap (denoted by reference si “G” in FIG. 1 of the Japanese publication) therebetween which corresponds to a height of the spacers, so that the original passing through the gap between the holder plate and the transparent plate can be prevented from being separated from the transparent plate by a distance larger than the height of the spacers.
Although a CCD (Charge Coupled Device) has been commonly used as the image reader of the above-described image reading apparatus, a CIS (Contact Image Sensor) as well as the CCD is used as the image reader in recent years, due to its size and cost which are smaller and lower than those of the CCD. However, the CIS has a smaller depth of field than that of the CCD. Therefore, where the above-described holder plate with the spacers, as disclosed in the above-described Japanese publication, is provided in an image reading apparatus equipped with the CIS as the image reader, the image reading apparatus could not provide a satisfactorily high degree of accuracy in the image reading, because upward displacement of the original from the transparent plate within the spacing gap is allowed. That is, where the CIS is used as the image reader, the original has to be brought into dose contact with the upper surface of the transparent plate, i.e., an original supporting surface of the image reader, thereby requiring an arrangement in which the original is pressed onto the original supporting surface by a presser plate member or the like which is biased to be brought into contact with the original.
It is common that a feeding device for feeding the original is built within the above-described cover body. For making the feeding device compact in size, it is also common that a feed path, along which the original is id from an original supply portion to an original exit portion via a reading position, is adapted to have a substantially U shape.
For obtaining a space available for piling up the originals which have exited through the original exit portion, it is common that the original exited portion is located in a position higher than the reading position, so that the original takes a posture inclined with respect to the original supporting surface, with a portion of the original closer to the original exit portion being given a position higher than a portion of the original closer to the reading position. Therefore, where the above-described presser plate member or the like is provided in the reading position, a force derived from a tension of the inclined original acts on the presser plate member in the upward direction, in a direction away from the original supporting surface. In this instance, if a biasing force acting on the presser plate member in the downward direction is not large enough to overcome the upward force, the original as well as the presser plate member is likely to be displaced upwardly. The upward displacement or separation of the original from the original supporting surface causes deterioration in the reading accuracy, particularly, where the CIS is used as the image, reader On the other hand, if the biasing force is adapted to be excessively increased, the excessively increased biasing force results in an increase in resistance against sliding movement of the original between the presser plate member and the transparent plate, thereby making it impossible to permit the original to enter between the presser plate member and the transparent plate, particularly, where the original is provided by a thin paper sheet.